2.1 Weed Control
The use of herbicides for controlling weeds or plants in crops has become almost a universal practice. The market for these herbicides approaches a billion dollars annually. Even with this extensive use, weed control remains a significant and costly problem for the farmer.
Present day herbicides used singly or in so-called tank mixes require good management to be effective. Time and method of application and stage of weed plant development are critical to getting good weed control with herbicides. Some weed species are simply resistant to today's herbicides. Therefore, the production of effective herbicides increases in importance every year, especially as other weeds are controlled and thus reduce competition. Application of large amounts of marginally effective herbicides on these weeds can result in a commitment to grow the same crop in subsequent years because of chemical persistence in the soil which prevents rotation with a crop sensitive to that herbicide.
Other herbicides, while not used directly to control weeds in field crops, are used as"total vegetation control agents" to entirely eliminate weeds in certain railroad and industrial situations. These herbicides may be deposited on areas where crops are planted by water run-off, or other natural means. Thus, in fields affected by run-off from land on which total vegetation control agents have been used, sensitive field crops may be killed or their growth seriously inhibited.
Herbicides with greater potency, broader weed spectrum and more rapid degradation in the soil would have a significant impact on these problems. Unfortunately, these compounds also have greater crop phytotoxicity. Crop hybrids or varieties with resistance to the compounds would provide an attractive solution by allowing the compounds to be used without risk of damage to the crop.